In information recording card including an ID card and a credit card, magnetically or optically reading methods have been widely used. However, the techniques are popularized and the data in the cards is easily altered or forged cards are spread, and there are increasing cases where people actually suffer damage from the forged cards, causing social problems about the privacy of personal information. For this reason, in recent years, as a material for controlling personal data, an IC card having an IC chip incorporated into a substrate for card made of a resin has drawn attention since it has a large data capacity and it can contain coded data.
For exchanging information between an IC circuit and an external data processing apparatus, the IC card has a connection terminal for electrically and mechanically connecting them. Therefore, the IC card has various problems in that the airtightness in the IC circuit must be secured, an electrostatic discharge damage is avoided, a failure of the electrical connection between terminal electrodes is likely to occur, and the mechanisms of the reader/writer are complicated. In addition, a manual operation of inserting or putting an IC card into or on a reader/writer is inevitably needed, and therefore the efficiency is low or the operation is burdensome in some business. Therefore, there has been desired the development of non-contact IC cards which need no burdensome operation and which can exchange information with a portable remote data processing apparatus.
For meeting the demand, a non-contact IC card which has an antenna utilizing electromagnetic waves and an IC chip having a memory and a calculation function in a substrate for card has been developed. In this IC card, the IC is driven by the induced electromotive force excited in the antenna in the card substrate by external electromagnetic waves from a reader/writer, and no battery power source is required in the card, and thus a card having excellent activity can be provided. According to applications, attempts are made to incorporate a thin battery, such as paper battery, into the card to enlarge the communication distance or to utilize higher frequency bands, but, from the viewpoint of reduction in the cost and widening applications, cards requiring no battery are strongly desired.
For recording information onto these cards, digital recording is conducted by a recordable IC chip provided on part of the card. For display or reading of the data recorded on the card, it is necessary to read the recorded data by means of a special reading apparatus, and therefore general users cannot read the data by themselves. For example, in membership cards in which a high premium or a point is put on members, information by an information note or the like is separately required if it is merely recorded onto the card. Therefore, demands of easy display of the recorded data are increasing.
For meeting the demands, technique has been developed in which a reversible display layer (for example, reversible heat-sensitive recording layer; hereinafter, referred to simply as “heat-sensitive recording layer”) is provided on the surface of the card substrate wherein the reversible display layer is of a polymer/low-molecule-type and includes an organic low molecule dispersed in a resin binder, and achieves display by utilizing the opaque-transparent contrast. The polymer/low-molecule-type reversible display medium is constituted by a support, e.g., a plastic sheet/colored layer/recording (polymer/low-molecule) layer/protecting layer.
Further, recently, for reducing the cost, a bare chip mounting method is attempted in which an IC chip is directly mounted on the card by providing an electrode portion for connecting an antenna to the IC chip on a sheet-form insulating substrate. In this case, a face down bonding method is employed in which a protrusion called bump is formed from solder or gold on an electrode portion on the circuit-formed surface of the IC chip, and connection is made to the electrode portion through the bump. The connection is made for filling the gap between the IC chip circuit surface and the insulating substrate with an an isotropic conductive film, a resin containing conductive particles, such as an anisotropic conductive resin, or under filling material.
By the way, in the IC cards, for securing reliability of the IC chip operation, the IC chip is protected by a sealing resin having a hardness different from that of the card substrate. Further, for avoiding an accident that the IC chip is mechanically broken leading to lose all data, a task is to improve the IC card in mechanical strength with respect to bending and a point pressure caused by impact at a point or the like. For achieving the task, a structure such that a reinforcing sheet is provided on the sealing resin to prevent the connection portion of the IC chip or the IC chip itself from being broken is considered.
A general process for producing the IC card is conducted in accordance with, for example, the following procedure. First, a resin sheet is printed by a known printing method, such as offset printing, gravure printing, or screen printing, and protecting sheets comprised of a thin film resin having high transparency are laminated on both surfaces of the printed resin sheet. Then, an IC module is disposed between these sheets and they are integrated by hot melting by means of a hot press, and punched out using a die having a predetermined size into a card form. Then, the card is embossed to make characters called embossed characters, and supplied to users.
However, the above-mentioned IC card having a reinforcing material poses the following problem. Specifically, when the reinforcing sheet and the sealing resin having a cure shrinkage behavior are used in combination, the reinforcing sheet deforms due to the cure shrinkage of the sealing resin. For this reason, when the IC module having the reinforcing sheet disposed on the IC chip sealed by the sealing resin is sealed between the resin sheets (card substrate), the deformation of the reinforcing sheet cannot be satisfactorily cancelled by the card substrate, so that the surface of the card substrate may become uneven.
In the card substrate having an uneven surface, when a printing operation is conducted with respect to the heat-sensitive recording layer, a spacing is caused between the heat-sensitive recording layer and a thermal head, so that the heat-sensitive recording layer cannot be satisfactorily heated, leading to a problem that missing of image recording is likely to occur.
An object of the present invention is to provide an IC card which can surely protect the IC chip by a reinforcing sheet while securing surface flatness of the card substrate, thus making it possible to surely achieve printing with respect to the reversible display layer provided on the surface of the card substrate.